In usual manner, fan blades made of composite material, in particular using carbon fibers, are made from a stack of pre-impregnated unidirectional plies which are placed in a mold with the successive plies being oriented differently, prior to compacting and polymerizing in an autoclave. That technique is very difficult and requires plie-stacking operations to be performed manually, which is lengthy and expensive.
Proposals have also been made to prepare woven preforms using dry fibers which are subsequently assembled together by stitching, prior to being impregnated with resin by injection into a closed mold. An alternative has consisted in making a single woven preform which is assembled together with one or more solid inserts prior to injection. Those techniques (U.S. Pat. No. 5,672,417 and U.S. Pat. No. 5,013,216) nevertheless present the drawback of requiring a plurality of parts to assembled together and of creating, in such assemblies, zones constituting privileged sites for weakness, e.g. by delamination, which is very harmful in terms of mechanical strength, in particular for ability to withstand impacts.